The broad objective of these studies is to evaluate the possible participation of calcium ion as an intracellular messenger mediating hormone action on adipose tissue cells. Several studies have suggested that calcium acts at a step(s) prior to formation of cyclic AMP by enhancing the activation of adenylate cyclase in adipocytes stimulated with lipolytic hormones. Experiments are proposed to test this hypothesis by measuring cyclic AMP levels and lipolysis in adipocytes exposed to various hormones and to determine the relation between cellular cyclic AMP and lipolysis in the presence or absence of calcium. Subsequent studies are designed to determine if calcium is acting within adipocytes. These studies will employ various pharmacologic agents which either promote (A23187 and X537A) or retard (verapamil and D600) calcium entry into cells. Another series of experiments is designed to prepare adipocyte-membrane "ghosts" filled with Ca ions-EGTA buffers which will "clamp" the intracellular calcium concentration at any desired level. By studying hormone activation of adenylate cyclase in such a preparation we hope to determine the relative roles of intra- and extracellular calcium in control of cyclic AMP formation. Lastly, studies are proposed to determine if hormones influence the distribution of calcium in adipocytes and if changes in the influx and/or the efflux of calcium into adipocytes is a necessary concomitant to hormone regulation of lipolysis and cyclic AMP formation.